.\"	$NetBSD: hardclock.9,v 1.3 2010/03/25 15:17:38 jruoho Exp $
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.\" by Thomas Klausner.
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.Dd February 27, 2023
.Dt HARDCLOCK 9
.Os
.Sh NAME
.Nm hardclock
.Nd real-time timer
.Sh SYNOPSIS
.Ft void
.Fn hardclock "int cnt" "int usermode"
.Sh DESCRIPTION
The
.Fn hardclock
function is called periodically based on pending work.
The rate ranges from
.Va hz
times per second on a very busy system, to twice a second on an idle system.
The
.Fa cnt
argument reports an estimate of the number of ticks since the last call.
Over long timescales, the average sum of
.Fa cnt
over one second is
.Va hz .
See
.Xr hz 9
for important details over shorter time scales.
The
.Fa usermode
argument is non-zero when
.Fn hardclock
is called from an context that interrupted usermode execution.
.Pp
.Fn hardclock
may perform different tasks such as:
.Bl -bullet -offset indent
.It
Run the current process's virtual and profile time (decrease the
corresponding timers, if they are activated, and generate
.Li SIGVTALRM
or
.Li SIGPROF ,
respectively).
.It
Increment the time-of-day, taking care of any
.Xr ntpd 8
or
.Xr adjtime 2
induced changes and leap seconds, as well as any necessary
compensations to keep in sync with PPS signals or external clocks, if
supported by the kernel.
.It
Schedule softclock interrupts
.Po
.Xr swi 9
.Pc
processing.
.It
Collect
.Xr hwpmc 4
statistics.
.It
Do device polling, when enabled
.Po
see
.Xr polling 4
.Pc .
.It
Implement software
.Xr watchdog 9
processing.
.It
Enqueue
.Xr epoch 9
processing.
.El
.Sh SEE ALSO
.Xr adjtime 2 ,
.Xr ntp_adjtime 2 ,
.Xr signal 3 ,
.Xr hwpmc 4 ,
.Xr polling 4 ,
.Xr ntpd 8 ,
.Xr epoch 9 ,
.Xr eventtimers 9 ,
.Xr hz 9 ,
.Xr swi 9 ,
.Xr watchdog 9
